Automated information storage and retrieval jukeboxes and systems (also known as libraries) are widely used to store large amounts of data on recordable media, such as magnetic tape or optical disk. Each piece of media is generally housed in a case or cartridge and stored in one of many cells in the library. When a host device requests that data be read from or recorded to a particular tape or disk, a library controller directs a robotic accessor to retrieve the desired cartridge from its storage cell and transport it to a drive unit inside the library. When the read or write operation is completed, the accessor removes the cartridge from the drive and returns it to a cell.
Several means have been developed to enable the accessor to retain a cartridge for transporting. One such means is a mechanical "hand" or gripper attached to the accessor to physically grasp and hold the desired cartridge. A gripper requires relatively complicated and space consuming mechanical elements which are prone to wear. The gripper also requires a sensor, such as a switch or a photodetector, and related control circuitry to detect the presence of the selected cartridge.
Another means, which reduces some of the problems associated with a mechanical gripper, is an electromagnetic picker. When the accessor is close to the selected cartridge, current is generated through an electromagnet creating a magnetic field to attract and hold a magnetically attractable label fixed to the cartridge. Like the mechanical gripper, the electromagnetic picker also requires a sensor to detect the presence of the selected cartridge. Moreover, to ensure that the cartridge is magnetically attached to the electromagnet and will remain there while being transported, a high current is required to generate the magnetic field. It will be appreciated that high current can cause heating and necessitate dissipation measures as well as increase the power requirements of the library accessor.